


A Hard to Swallow Proof

by 3DrotTMNT



Category: Rise of the Teenage Mutant Ninja Turtles (Cartoon 2018)
Genre: Alternate Universe, Blood and Gore, Gen, Serious Injuries, Temporary Character Death, parasite au, this fic was stuck on my drive for too long
Language: English
Status: Completed
Published: 2020-09-16
Updated: 2020-09-16
Packaged: 2021-03-06 22:46:47
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence, Major Character Death
Chapters: 1
Words: 1,494
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26486635
Author URL: https://archiveofourown.org/users/3DrotTMNT/pseuds/3DrotTMNT
Summary: Leo knew there was something weird with his nerd older brother Donatello. He was convinced the purple one wasn't himself. He tried to tell Raph and Mikey about it but none of them listens. He needed to show them the truth. He needed to find proof.
Comments: 7
Kudos: 39





	A Hard to Swallow Proof

**Author's Note:**

> This one-shot has been written just after I've heard of a Parasite AU concept idea where a parasite takes control of Donnie's body and mind. This AU is not mine, it belongs to @amyhaunter and @CptMop and what you're about to read is not even canon in their AU. It's really just a random fic written at 3am.
> 
> Also, there is a graphic gory scene at the end, hence the warning, so be careful.
> 
> Enjoy :)

"This is absurd, Leo." Raph sighed as he walked out of the kitchen, tired to hear his brother repeating the same nonsense. It has been a while since the blue turtle started reporting every single Donnie's behaviour he found "weird", "out of normal", accusing him to not be the "real Donnie".

"Raph, please!" Leo pleaded out of breath. It was hard for him to follow his older brother who was making one step while he could only make four. "I'm not lying. I would have given up a while ago if it was just a joke."

Mikey, who was following close behind Leo, rolled his eyes. "Just a few days? You've held on jokes longer than this. Your record is a whole year, Leon."

"Okay, fine. I'm a jokester, but-" He ran to step in front and stop the snapping turtle. "I am dead serious." 

He looked at Raph straight in the eyes. If words couldn't convince him, maybe his expression could. He wasn't faking. The red one stared back at him, examining him as if he was waiting for Leon's typical "Gotcha!". Raph's gaze left to focus on something entering the main room. " Then why don't we just ask him?"

Blue turned suddenly to see Donnie, completely distracted by his phone, coming to their direction.

"Hey, D!" Mikey waved over Raph's shoulders. 

Donatello glanced at him, keeping his head down his screen. "Oh. Mornin', Angelo." He then put down his phone. "Why are you three standing here?"

Leo frowned. The way he casually spoke irritated him. His brothers refused to believe him, but they accepted this thing's lies. It was unbearable.

"Just resolving a dilemma," Raph answered, slightly smirking.

"Why didn't you tell me sooner?" The softshell raised an eyebrow. "That is my speciality."

Disgusting. His voice. His manners. His egocentrism. All of it mimicked perfectly. 

"Well," Red started, putting his hand on Leo's head "our dear brother here present believes that you are... What was it again?" He faked forgetting, letting time to Mikey to say it for him.

"A parasite who took over Donnie's body, copying his every action to replace him inside our family."

"Oh, right! That."

Donnie showed a surprised expression then fell to a long sigh. "This again? Leonardo. Me having different obsessions as you doesn't mean I've been possessed by a demon or turned into a zombie, or even… taken over by a parasite."

"Did you get your answer, Leo?" Raph patted Leo's head. "Will you now stop with those ridiculous accusations?"

Obviously. It would have been too easy. The fake Donnie was never going to reveal itself by simply asking. 

He removed Raph's big hand. "No way!" He pointed at the purple one. "That thing is not our brother and I'll prove it."

"An interrogation!" Orange yelled, taking the situation lightly. "We can ask him some questions about his past and deepest secrets! Only the real Donnie would be able to answer."

"If it'll make Leo finally shut it," Raphael said, exasperated. "Let's go for it."

Mikey seemed so excited for unknown reasons. It wasn't a game. Leo was trying his best to show his brothers the truth, yet here they were. Asking random questions to the impostor.

"When did you stop wearing glasses?" The box turtle asked, tippy-tapping his finger on his chin.

Donnie didn't wait to answer. "When I was nine and four months. We started to go outside more frequently, consequently, I accidentally broke three pairs in a week. It was obviously more adequate to use contact lenses."

"Uh-huh… And…" Mikey searched for another one. "What is your computer password?"

"The new or old password?"

"You got a new password?"

"Exact. Because as soon as I told you my old password, which was BootyyyyShaker9000 to answer the question, everybody was aware of it, including the Purple Dragons."

Raph glared at Leo. The responses were flawless. Evidently, that thing learned Donnie well. His memories have been registered. Asking about them was useless. So, Blue decided to ask the next one.

"What do you think of your shell?"

The question put everything in a heavy silence.

"... I remember asking you to not talk about it." The softshell said while bringing his left hand on his battleshell.

He was avoiding the answer! Wasn't it a proof that this wasn't Donnie at all? Leonardo proudly turned to Raph who gave him a deadly gaze.

Oh.

He grabbed his little brother by his shell, to be face to face with him. "Leo! That is ENOUGH! You are going off-limits! Whatever scenario you invented gotta stop." 

Michelangelo, who calmed down after the last question, felt guilty. "Sorry, Dee. We went too far."

"That is not your fault, Mikey," Raph reassured him, without leaving Leo's gaze. "It's his." He abruptly put him down on his feet. "He should apologise."

Should he? He was only trying to help them see the truth! Or was he wrong…?

"Donnie. I'm… sorry for bringing up a forbidden subject." He mumbled, head staring at the floor, forced by the heavy and menacing look the oldest was giving him.

Donatello crossed his arms, taunting him. "And?"

"And… for calling you a «fake»…" He mostly didn't think any of those words. But he lacked solutions. He didn't know what to do.

"Well, I forgive you," Purple said. "You've watched too many JJ movies, 'nardo. I guess we'll put the fault on those and forget about this little incident."

Blue was about to give up as they were probably right. And they were, on one point.

"JJ movies were real…"

In a move, he grabbed his ōdachi resting on his shell and pointed it at Donnie who took a step backwards, raising his hand above his shoulders.

"Leo, what are you doing?" Mikey cried out.

"There are other ways to prove you I'm right."

"LEO! PUT THAT DOWN!" Raphael shouted out of anger.

"It's fine, brothers," Donatello calmly said, lowering his hands. "He won't do anything. We know Leo, right?"

Leonardo's grip tightened. His arms were shaking and his hands sweaty. He couldn't do it. But it was so infuriating.

"That's not your voice…" He muttered teeth clenched.

"Leo, you're not talking sen-"

"That's not YOUR voice!" He growled louder, tears overflowing out his eyes. "Not YOUR body. It's not YOURS!"

The way he yelled, full of fear and hatred, worried Raph and Mikey. However, Donnie kept his serious tone.

Leo blinked four or five times, trying to remove the tears that were blurring his sight. He kept staring at the impenetrable look the thing on the other side of the sword retained. 

Slowly, it changed. It smirked, so slightly only Leo noticed it.

"But it is mine, Leo."

That thing was playing with him and wasn't even trying to hide, at least not to the blue one. It was playing with his nerves. 

His hands twitching more than ever, his heart beating faster and faster, he stepped back.

He gained momentum and ran towards the softshell, his blade piercing its plastron and travelling all the way through until touching the battleshell.

"LEO!!! WHAT THE-" Raph screamed, pulling Leo back. He immediately grabbed Donnie before he fell on the ground, his arms and legs completely numb.

They'll see, Leo thought as his older brother was checking the thing's inert body.

They'll see, he thought as Mikey, grabbing his arm, was falling on his knees, cries mixed with screams.

"ARE YOU OUT OF YOUR BLOODY MIND, LEO?!" 

Raphael put his temple against Donnie's chest, looking for a heartbeat. He barely heard anything. Maybe one or two out of sync. He pressed harder to better listen and concentrate, desperately seeking a sign of life. He could swear he heard something, yet he couldn't analyse it, at least the hand grabbing his head didn't let him.

" _oOOoh I didn'T ThiNk you'D Do it, lEOnarDo_." The lifeless body slowly moved, giggling in a dreadful voice. Its hand clenched harder on Raph's head who screamed in pain. "i MIgHt haVE uNderESTimated yoU."

He was right! He unmasked that creature. But at what cost, now it had Raph. The last was trying with all of his strength to remove the fake Donnie's hand out of his head, but it didn't move at all, not even an inch. It only tightened its grip. He felt like his skull was about to crack.

Leo, still his sword in hand, slicing its wrist, Raph falling over one side, and Donnie the other.

The sick creature, now on its shell, proudly admired its slashed arm, black blood dripping down.

" _whAT dID yoU thOuGHT YoU'd acHIeve!_ " It maniacally laughed.

When Leo turned to his older brother, this one was still combating with the hand. It was now scratching his eyelids and attempting to enter his eye socket. His screams were echoing against the lair's walls, completely deafening.

The hand made its way through.

And it kept laughing, its laughs growing louder than Raph screams.

Or was Raph laughing too?

**Author's Note:**

> After sharing this fic ([and a quick drawing related to it](https://twitter.com/3DrotTMNT/status/1293580072042078208?s=20)), I've received many messages asking to know more about this AU. So, before you ask, I'll answer :)
> 
> I do not own this AU, therefore I cannot explore this idea any further. If you want it to be a real thing, encourage Mop and/Amy to do so! It is for now just a concept.
> 
> Thank you for reading!  
> I hope you liked it!


End file.
